Two main areas are currently under investigation; endocrine mechanisms for the control of lymphoma and mammary tumor. Morphologic differences have been found between P1798 lymphoma sensitive to glucocorticoid and those resistant to such treatment. The main difference lies in the presence of a cationic binding coat on the outside of the cell membrane of cells from a tumor sensitive to glucocorticoid. This allows ultramicroscopic examination after staining with Alcian Blue to distinguish between the two types of tumor. Unpublished studies relating to the difference between fucose-containing macromolecules of cell membrane preparations are in progress, but already show significant differences between the two types of cells, sensitive and resistant, when examined by a double isotope technique. Evidence has been presented which is not consistent with the current notion that glucocorticoid administration inhibits macromolecular synthesis by inhibiting glucose transport. Conditions have been found under which cortisol clearly inhibits uridine transport and incorporation when no transport is found. In fact, the inhibition of uridine transport can be demonstrated in the absence of glucose from the incubation medium. Conditions have been found which transform MTW9, a transplantable oophorectomy non-responsive tumor requiring a high serum prolactin for growth, into a tumor which regresses after oophorectomy.